Year	Percent
1991	36.616
1992	36.595
1993	36.404
1994	36.068
1995	35.619
1996	34.898
1997	33.604
1998	32.971
1999	32.239
2000	31.432
2001	30.93
2002	30.429
2003	29.958
2004	29.563
2005	29.267
2006	28.846
2007	22.664
2008	22.399
2009	22.136
2010	21.864
2011	21.613
2012	21.328
2013	21.031
2014	20.746
2015	20.477
2016	19.966
2017	19.527
2018	19.071
2019	18.611
2020	18.154
2021	17.692
2022	17.235